Color tunable light source module with brightness and dimming control
First Claim
1. A method of controlling brightness and color temperature in a light source device having a plurality of independently addressable groups of LEDs, wherein the LEDs in each group emit light of a different color, the method comprising:
- receiving a control signal indicating that a brightness of the light source should be changed from a starting brightness value to a target brightness value;
defining a brightness trajectory from the current brightness value to the target brightness value, the brightness trajectory consisting of a sequence of frames, each frame having a different brightness value assigned thereto and a duration that is long enough to be perceptible to a human eye; and
executing the brightness trajectory, wherein executing the brightness trajectory includes, for each frame in the sequence of frames;
determining, using a microcontroller, a brightness set-point for the current frame based at least in part on the brightness trajectory;
computing, for each of a plurality of output channels of the microcontroller, a pulse width and a number of pulses to include in a pulse train to be generated on each of the plurality of output channels during a brightness cycle that is common to all of the output channels, the brightness cycle consisting of a fixed number (NB) of pulse periods, each pulse period having the same duration (p), the pulse train on each output channel consisting of a selectable number (NON) of active pulse periods of duration p during each of which a pulse having a selectable pulse width is generated and another number (NB−
NON) of inactive pulse periods of duration p during which a pulse is not generated, the computation being based at least in part on a current color temperature and the brightness set-point for the current frame such that the pulse width for each output channel is computed based on the current color temperature and the number NON of active pulse periods is computed based on the brightness set-point,wherein selecting the number NON of active pulse periods and the pulse width for each output channel includes;
accessing a lookup table using the current color temperature to determine first and second baseline pulse width parameters;
interpolating between the first and second baseline pulse width parameters to generate a width value consisting of a first subset of most significant bits and a second subset of least significant bits;
determining the pulse width based at least in part on the most significant bits of the width value; and
determining the number NON of pulses to include in the pulse train based at least in part on the brightness set point and the least significant bits of the width value;
generating, on each of the plurality of output channels, a pulse train using the pulse width and number of pulses computed for that channel;
converting each of the pulse trains to an operating current;
delivering each of the operating currents to a different one of the independently addressable groups of LEDs; and
repeating the acts of generating, converting and delivering for the duration of the frame.
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Abstract
LED-based light source modules can incorporate color tunability and brightness control, allowing a user to select a desired color temperature and/or brightness and to change either or both dynamically. An emitter can include multiple independently addressable groups of LEDs, each emitting light of a different color. By controlling the relative operating current provided to each group, a desired color temperature can be achieved, and by controlling the absolute operating currents, the brightness of the output light can be controlled. Pulse width modulation (PWM) can be used to control the relative and absolute operating currents. Smooth, gradual transitions between brightness and/or color temperature settings in response to changes can be provided.
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Citations
21 Claims
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1. A method of controlling brightness and color temperature in a light source device having a plurality of independently addressable groups of LEDs, wherein the LEDs in each group emit light of a different color, the method comprising:
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receiving a control signal indicating that a brightness of the light source should be changed from a starting brightness value to a target brightness value; defining a brightness trajectory from the current brightness value to the target brightness value, the brightness trajectory consisting of a sequence of frames, each frame having a different brightness value assigned thereto and a duration that is long enough to be perceptible to a human eye; and executing the brightness trajectory, wherein executing the brightness trajectory includes, for each frame in the sequence of frames; determining, using a microcontroller, a brightness set-point for the current frame based at least in part on the brightness trajectory; computing, for each of a plurality of output channels of the microcontroller, a pulse width and a number of pulses to include in a pulse train to be generated on each of the plurality of output channels during a brightness cycle that is common to all of the output channels, the brightness cycle consisting of a fixed number (NB) of pulse periods, each pulse period having the same duration (p), the pulse train on each output channel consisting of a selectable number (NON) of active pulse periods of duration p during each of which a pulse having a selectable pulse width is generated and another number (NB−
NON) of inactive pulse periods of duration p during which a pulse is not generated, the computation being based at least in part on a current color temperature and the brightness set-point for the current frame such that the pulse width for each output channel is computed based on the current color temperature and the number NON of active pulse periods is computed based on the brightness set-point,wherein selecting the number NON of active pulse periods and the pulse width for each output channel includes; accessing a lookup table using the current color temperature to determine first and second baseline pulse width parameters; interpolating between the first and second baseline pulse width parameters to generate a width value consisting of a first subset of most significant bits and a second subset of least significant bits; determining the pulse width based at least in part on the most significant bits of the width value; and determining the number NON of pulses to include in the pulse train based at least in part on the brightness set point and the least significant bits of the width value; generating, on each of the plurality of output channels, a pulse train using the pulse width and number of pulses computed for that channel; converting each of the pulse trains to an operating current; delivering each of the operating currents to a different one of the independently addressable groups of LEDs; and repeating the acts of generating, converting and delivering for the duration of the frame. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A light source module comprising:
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an emitter having a plurality of LEDs disposed on a single substrate, the plurality of LEDs being electrically connected into at least three independently addressable groups of LEDs, wherein the LEDs in each group emit light of a different color; a plurality of current regulators, each current regulator being coupled to provide an operating current to a different one of the independently addressable groups of LEDs in response to an adjustable input voltage and a constant reference voltage; a microcontroller configured to receive input settings specifying a color temperature and a brightness setting and to generate a pulse train on each of a plurality of output channels, each pulse train including a selectable number of pulses having a selectable pulse width, wherein the microcontroller is further configured to select the number of pulses and the pulse width for each output channel based on the input settings; and a plurality of RC integrator circuits, each RC integrator circuit being coupled between a different one of the output channels of the microcontroller and a different one of the plurality of current regulators, each RC integrator circuit being coupled to receive the pulse train from a different one of the output channels of the microcontroller and to provide the adjustable input voltage to a different one of the current regulators, the microcontroller being further configured to; determine from the received input settings that a brightness of the light source should be changed from a starting brightness value to a target brightness value; define a brightness trajectory from the current brightness value to the target brightness value, the brightness trajectory consisting of a sequence of frames, each frame having a different brightness value assigned thereto and a duration that is long enough to be perceptible to a human eye; and execute the brightness trajectory by generating, during each frame, a series of pulse trains based on the brightness value assigned to that frame, wherein generating a series of pulse trains includes computing, for each of the output channels, a pulse width and a number of pulses to include in each pulse train to be generated on that one of the output channels during a brightness cycle that is common to all of the output channels, the brightness cycle consisting of a fixed number (NB) of pulse periods, each pulse period having the same duration (p), the pulse train on each output channel consisting of a selectable number (NON) of active pulse periods of duration p during each of which a pulse having a selectable pulse width is generated and another number (NB−
NON) of inactive pulse periods of duration p during which a pulse is not generated, the computation being based at least in part on a current color temperature and the brightness set-point for the current frame such that the pulse width for each output channel is computed based on the current color temperature and the number NON of active pulse periods is computed based on the brightness set-point,and wherein selecting the number NON of active pulses and the pulse width for each output channel includes; accessing a lookup table using the target color temperature to determine first and second baseline pulse width parameters; interpolating between the first and second baseline pulse width parameters to generate a width value consisting of a first subset of most significant bits and a second subset of least significant bits; determining the pulse width based at least in part on the most significant bits of the width value; and determining the number NON of pulses to include in the pulse train based at least in part on the brightness set point and the least significant bits of the width value. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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Specification